Theodore Roosevelt Jr. (/ˈroʊzəvɛlt/ ROH-zə-velt;[a] October 27, 1858 – January 6, 1919), often referred to by his initials TR, was an American politician, author, naturalist, soldier, explorer, and historian who served as the 26th President of the United States. He was a leader of the Republican Party and founder of the Progressive Party insurgency of 1912. He is known for his exuberant personality, range of interests and achievements, and his leadership of the Progressive Movement, as well as his "cowboy" persona and robust masculinity. Growing up, Roosevelt was a sickly child who suffered from asthma. To overcome his physical weakness, he embraced a strenuous life. He was home-schooled and became an eager student of nature. He attended Harvard College, where he studied biology, boxed, and developed an interest in naval affairs. He quickly entered politics, determined to become a member of the ruling class. In 1881, he was elected to the New York State Assembly, where he became a leader of the reform faction of the GOP. His book, The Naval War of 1812 (1882), established him as a learned historian and writer.